linux-kernel - [PATCH 2/3] sparc: gup_pte_range() support THP based tail recounting

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Message-Id: <1318862517-7042-3-git-send-email-aarcange@redhat.com>
Date:	Mon, 17 Oct 2011 16:41:56 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Michel Lespinasse <walken@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Shaohua Li <shaohua.li@...el.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH 2/3] sparc: gup_pte_range() support THP based tail recounting

Up to this point the code assumed old refcounting for hugepages
(pre-thp). This updates the code directly to the thp mapcount tail
page refcounting.

Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
---
 arch/sparc/mm/gup.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
index a986b5d..afcebac 100644
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -12,6 +12,17 @@
 #include <linux/rwsem.h>
 #include <asm/pgtable.h>
 
+static inline void get_huge_page_tail(struct page *page)
+{
+	/*
+	 * __split_huge_page_refcount() cannot run
+	 * from under us.
+	 */
+	VM_BUG_ON(page_mapcount(page) < 0);
+	VM_BUG_ON(atomic_read(&page->_count) != 0);
+	atomic_inc(&page->_mapcount);
+}
+
 /*
  * The performance critical leaf functions are made noinline otherwise gcc
  * inlines everything into a single function which results in too much
@@ -56,6 +67,8 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 			put_page(head);
 			return 0;
 		}
+		if (head != page)
+			get_huge_page_tail(page);
 
 		pages[*nr] = page;
 		(*nr)++;
--
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